The present invention relates to an X-ray CT apparatus which is a medical X-ray CT (Computed Tomography) apparatus or an industrial X-ray CT apparatus and which holds operations of an X-ray data acquisition system or information for imaging conditions and performs image reconstruction based on the same, upon a conventional scan (axial scan), a cine scan, a helical scan, a variable-pitch helical scan or a helical shuttle scan.
An X-ray CT apparatus acquires X-ray projection data by scanning a subject with X rays and image-reconstructs a tomographic image of the subject, based on the X-ray projection data (refer to, for example, Japanese Unexamined Patent Publication No. 2004-173756).
Such an X-ray CT apparatus has a two-dimensional X-ray area detector of a matrix structure typified by, for example, a multi-row X-ray detector or a flat panel. Upon data acquisition by a conventional scan (axial scan), a cine scan or a helical scan, a scanning table is changed in a z direction by the operation of an X-ray data acquisition system during scan to perform X-ray data acquisition. In the case of a variable-pitch helical scan and a helical shuttle scan, an absolute coordinate position or a relative coordinate position of a z-direction coordinate of the scanning table is recorded for each view or at several views as position information of the scanning table. Described specifically, when a scanning table velocity changes like v(t) as shown in FIG. 16, a scanning table position changes like z(t) and a data acquisition view number linearly increases like N(i). Therefore, for example, data of a scanning table position z(t1) is recorded so as to correspond to an N(t1) view. Incidentally, the data of the scanning table position z(t1) may be recorded with being added to X-ray projection data.
Here, an encoder for detecting a position is installed in the scanning table as in the case of a rotary encoder, a linear encoder or the like, and the installed encoder is used to obtain data about each position of the scanning table in real time during scan. For example, X-ray projection data and position data of the scanning table at the time that the X-ray projection data is obtained, are stored in association with each other. For example, as file data different from the X-ray projection data, the position data of the scanning table is stored in association with it each other. Thereafter, image reconstruction is carried out using the X-ray projection data and the position data of the scanning table both associated with each other, thereby to obtain a tomographic image of the subject.
Therefore, there is a case in which the addition of the X-ray projection data to each view is not easy. Further, there was a case where when z-direction coordinate information of the scanning table corresponding to each view was contained as another file, it was not easy to associate the z-direction coordinate information of the scanning table and each view for the X-ray projection data with each other upon image reconstruction.
Thus, there was a case in which a problem arose in that the association of the X-ray projection data and the scanning table z-direction coordinate information with each other upon the X-ray projection data acquisition or image reconstruction was not easy.
In an X-ray CT apparatus having a multi-row X-ray detector or an X-ray CT apparatus having a two-dimensional X-ray area detector typified by a flat panel, there is a tendency to increase the number of channels of an X-ray detector and increase the number of views for X-ray projection data as the resolution in a row direction rises. Further, there is a tendency to make the rotational velocity of the gantry fast. That is, the number of views per unit time trends to increase. A z-direction position of a scanning table or cradle is measured by the scanning table. Its z-direction position data is added to X-ray projection data obtained by a data acquisition system (DAS) of a scanning gantry rotating section at a scanning gantry fixing section. Therefore, this control becomes difficult due to the increase in the number of views per unit time.
Thus, an object of the present invention is to provide an X-ray CT apparatus capable of efficiently describing and storing position information and photography information of an X-ray data acquisition system by less parameters.